Burner with venturi tube and flow distributing elements

ABSTRACT

A burner fed with a flow of an air-fuel mixture, has a venturi tube arranged at the inside of a tubular burner body provided with through apertures through which said flow passes. The venturi tube is supported and centered in the body at one of its ends. Additional support and centering means of said venturi tube are provided at the inside of said tubular body. The additional support and centering means are provided with control means controlling the distribution of said flow of said air-fuel mixture.

The invention concerns a burner with Venturi tube, provided with flowdistributing elements.

In the burner equipped with Venturi tube, the fuel is fed at a certainpressure and speed to the mouth of the Venturi tube, causing theaspiration of a certain quantity of air, the so-called primary air,which is mixed to the fuel at the inside of the Venturi tube and, afterleaving the tube, is distributed to the slots of the burner diffuser.

The distribution of the mixture air-fuel to the slots of the burnerdiffuser is usually not uniform, thus generating a non-uniform flame andcausing both the flame to be detached from some areas of the diffuser,even in normal operating conditions, and the flame to be flattened onthe surface of some areas of the diffuser, which causes overheating ofsaid surface.

In addition, the Venturi tube is fixed to the diffuser at one end, forexample by means of welding, whilst the other end remains free.Therefore, the Venturi tube acts as a beam fixed at one end, bendingowing to its own weight and being subject to a danger of permanentstrains, caused, for example, by impacts or by temperature variations towhich the burner is subject during operation. The bending of the Venturitube aggravates the non uniformity of the distribution of the mixture tothe slots of the diffuser.

It is known from DE-2350846 a burner fed with a flow of an air-fuelmixture, comprising a Venturi tube arranged at the inside of a burnerbody provided with apertures through which said flow passes, saidVenturi tube being supported to said body at one of its ends and beingfurther supported two rows of baffles distributed through the wholelength of the burner. The baffles are capable of generating vortices inthe flow of air-fuel mixture flowing out of the Venturi tube in order toprevent solid impurities contained in the air-fuel mixture from reachingthe apertures of the burner body. The above mentioned baffles avoidbending of the Venturi tube but the formation of the vortices in theflow of air-fuel mixture due to the presence of the baffles isdetrimental to a uniform distribution of the air-fuel mixture to theapertures of the burner body.

U.S. Pat. No. 3,353,583 discloses a radiant burner fed with a flow of anair-fuel mixture, comprising a Venturi tube arranged at the inside of aburner body provided with an elongated aperture through which said flowpasses, said aperture being covered by combustion sustaining screenassembly, said Venturi tube being supported to said body at one of itsends and being further supported by a curved baffle having an end whichis aligned with a portion of the outlet of the Venturi tube andinterferes with the flow of the air-fuel mixture in order to divide theflow into two streams directed to different portions of said elongatedaperture. The baffle interferes with the flow of air-fuel mixture in theregion of the outlet of the Venturi tube, when the speed of the mixtureis relatively high, which implies a considerable turbulence in the flowof the mixture being generated, which increases the resistance of theburner and makes difficult to obtain a uniform distribution of themixture through the elongated aperture.

EP-A-0 217 470 discloses a burner for gas boilers fed with a flow of anair-fuel mixture, comprising a Venturi tube arranged at the inside of aburner body provided with apertures through which said flow passes, saidVenturi tube being supported to said body at one of its ends whilst theother end remains free. The burner is provided with a partitionextending in an axial direction and provided in a region remote fromsaid apertures with an opening, said partition being further providedwith a deflector which diverts the air-fuel mixture flowing or theVenturi tube in the direction of the opening in the partition. Thedeflector and the partition reduces the turbulence of the air-flowmixture flowing out of the venturi tube and improve the uniformity ofdistribution of the mixture to the apertures of the burner body. Howeverthe Venturi tube, which is supported only at one end, is subjected tobending stresses which reduce the life of the burner.

This invention intends to eliminate the above mentioned drawbacks.According to the invention there is provided a burner comprising atubular burner body, a Venturi tube arranged at the inside of saidburner body and supplying a flow of air-fuel mixture to the inside ofsaid bruner body provided with apertures through which said flow passesand generates a flame, one end of said Venturi tube being fixed to saidburner body, additional support and centring means provided with controlmeans for controlling the distribution of said flow of air-fuel mixtureto said apertures, said support and centring means having asubstantially flat shape, characterized in that said control meanscomprises openings defined in said support and centring means.

The invention will now be described with reference to the drawings,which illustrate, only by way of non-restrictive examples, someembodiments of the invention.

FIG. 1 is a longitudinal section of a burner according to the invention;

FIG. 2 in a section as in Figure, concerning a further embodiment of theinvention;

FIG. 3 is a cross section of FIG. 1, through a line III—III;

FIG. 4 is a cross section of FIG. 1, through a line IV—IV;

FIG. 5 is a cross section of FIG. 2, through a line V—V;

FIG. 6 is a cross section of FIG. 2, through a line VI—VI;

FIG. 7 is a longitudinal interrupted section as in FIG. 1, concerning astill further embodiment of a burner according to the invention;

FIG. 8 is a cross section of FIG. 7, through a line VIII—VIII.

With reference to the drawings, 1 denotes the body of a burner accordingto the invention, provided at the inside with a Venturi 2 tube fixed tothe body 1 at a first end 3, for instance by welding.

The body 1 of the burner is provided with apertures (not shown), forinstance shaped as slots, allowing an air-fuel mixture sucked throughthe Venturi tube 2 to pass from the inside to the outside of the body 1.

At the inside of the body 1, a first support and centring means of theVenturi tube 2 is arranged at an intermediate section of the Venturitube 2 and a second support and centring means is arranged at a secondend 6 of the Venturi tube 2.

The second support and centring means may be even arranged at a secondintermediate section of the Venturi tube 2. Said first 4 and second 5support and centring means are substantially flat, and havesubstantially the same shape of the outer outline, comprising twosubstantially rectilinear stretches 7, 8 (FIG. 3) connected by a firstinterconnecting stretch 9, having an outline substantially matching theouter outline of the Venturi tube 2, and a second interconnectingstretch 10 having a shape substantially matching the shape of the innersurface 16 of the body 1.

On the surface of said first support and centring means 4 and secondsupport and centring means 5 apertures 11 are made, allowing passage ofthe air-fuel mixture. The shape, dimensions and arrangement of saidaperture 11 are such as to obtain a flow of mixture which can becontrolled in any condition, after the mixture has passed through saidapertures 11, thus obtaining, for instance, a uniform flow through theslots of the body 1. Said apertures 11 may have, for example, a circularshape, a triangular shape or any other shape. A substantially uniformflow through the slots of the body 1 means a flow of mixture having aspeed vector with substantially constant, or in any event slightlydifferent, magnitude and direction for each slot. This makes possible toobtain uniform flames, in normal operating conditions of the burner,that is flames having a substantially constant height, which do notdetach from the surface of the burner and/or do not flatten on the body1, thus causing overheating of the latter, when operating conditions,such as the rate of flow of the mixture or fuel, or the type of fuelused, are changed.

FIGS. 2, 5 and 6 illustrate a further embodiment of said first 4 andsecond 5 support and centring means of the Venturi tube 2. In saidfurther embodiment, said first 4 and second 5 support and centring meansare fixed to respective annular means 12, 13 having a shapesubstantially matching the shape of the outline of the inner surface 16of the body 1, in order to make easier centring said means 4, 5 at theinside of the body 1.

FIGS. 7 and 8 illustrate a still further embodiment of the burneraccording to the invention, provided, for instance, at said second end 6of the Venturi tube 2, with support and centring means 14, 15 comprisinga ring 14 arranged on the Venturi tube 2 in contact with its outersurface, said ring being provided with a plurality of protrusions 15,for instance shaped as blades, facing toward the outside of the ring 14and substantially radially directed with respect to the axis

A of the burner. The ends of the protrusions 15 facing toward the innersurface of the body 1 lean against said inner surface and have anoutline shape substantially matching the shape of said inner surface.Said blade-shaped protrusions 15 are dimensioned, arranged and orientedin such a way as to obtain a substantially uniform flow, or, in anyevent, a controlled distribution of flow. All that being obtained due tothe inclination of the blades 15, which may be selected when planningthe burner, so as to obtain a controlled flow through the slots, afterthe mixture has passed through the spaces 17 defined between pair ofadjacent blades. For instance, each blade 15 may be arranged on a planeintersecting the axis of the burner at predetermined angle, which may bethe same, or different, for each blade. In addition, each blade may havea uniform width, or a width increasing toward the end which is incontact with the inner surface 16 of the burner 1. The protrusions 15shaped as blades may be part of the body of the Venturi tube 2, thusmaking possible not to use the ring 14. The surface of the blades may beflat or may be curved in a radial or and/or in an axial direction. Inthe latter case, the surface of each blade may have the same radii ofcurvature, or different radii.

The support and centring means 4, 5 and 14, 15 make possible to keep theVenturi tube centred with respect to the axis A of the burner, which isadvantageous for the purpose of controlling the flow of the air-fuelmixture through the slots and makes possible to limit the bending of theVenturi tube caused by its own weight or other stresses.

What is claimed is:
 1. A burner comprising; a tubular burner body, aventuri rube arranged at the inside of said burner body and supplying aflow of air-fuel mixture to the inside of said burner body, said burnerbody being provided with apertures through which said flow passes andgenerates a flame, one end of said venturi tube being fixed to saidburner body to support and center said venture tube at said one end,additional support and centering means of said venturi tube providedwith control means for controlling the distribution of said flow ofair-fuel mixture to said apertures, said support and centering meanshaving a substantially flat shape, said control means comprisingopenings defined in said support and centering means, and saidadditional support and centering means having first support andcentering means arranged at a first intermediate section of said venturitube and second support and centering means.
 2. A burner according toclaim 1, wherein said second support and centering means are arrangednear a second end of said venturi tube.
 3. A burner according to claim1, wherein said second support and centering means are arranged at asecond intermediate section of said venturi rube.
 4. A burner accordingto claim 3, wherein said second support and centering means has asubstantially flat shape.
 5. A burner according to claim 4, wherein saidcontrol means comprises openings defined in said second support andcentering means.
 6. A burner according to claim 5, wherein said openingshave a substantially circular shape.
 7. A burner according to claim 4,wherein said second support and centering means has an outer profilecomprising two substantially rectilinear stretches connected by a firstconnecting stretch, having a shape substantially matching the shape ofan outer outline of the venturi tube, and by a second connectingstretch, having a shape substantially matching the shape of an outlineof the inner surface of the body.
 8. A burner according to claim 5,wherein said second support and centering means is associated to ringmeans having a shape substantially matching the shape of the outline ofthe inner surface of the body.
 9. A burner according to claim 1, whereinsaid first support and centering means has an outer profile comprisingtwo substantially rectilinear stretches connected by a first connectingstretch, having a shape substantially matching the shape of an outeroutline of the venturi tube, and by a second connecting stretch, havinga shape substantially matching the shape of an outline of an innersurface of the body.
 10. A burner according to claim 1, wherein saidfirst support and centering means is associated to ring means having ashape substantially matching the shape of an outline of an inner surfaceof the body.
 11. A burner according to claim 1, wherein said controlmeans comprises protrusions of said first support and centering means,said protrusions being aligned in a substantially radial direction withrespect to a longitudinal axis of the burner, said openings beingdefined between adjacent pairs of said protrusions.
 12. A burneraccording to claim 11, wherein said first support and centering meanscomprises ring means arranged on the venturi tube in contact with itsouter surface, said ring means being provided with said protrusions. 13.A burner according to claim 11, wherein said protrusions are part of thebody of the venturi tube.
 14. A burner according to claim 13, whereineach of said protrusions has an end facing toward an inner surface ofthe body and leaning against said inner surface.
 15. A burner accordingto claim 14, wherein said end has an outline having a shapesubstantially matching the shape of said inner surface.
 16. A burneraccording to claim 13, wherein said protrusions are substantially bladeshaped.
 17. A burner according to claim 16, wherein each of saidsubstantially blade shaped protrusions lies on a respective planeintersecting said longitudinal axis at a predetermined angle.
 18. Aburner according to claim 17, wherein said predetermined angle is thesame for each of said substantially blade shaped protrusions.
 19. Aburner according to claim 17, wherein said predetermined angle is notthe same for each of said blade shaped protrusions.
 20. A burneraccording to claim 16, wherein said blade shaped protrusion have aconstant width.
 21. A burner according to claim 16, wherein said bladeshaped protrusions have a width increasing toward said end facing towardsaid inner surface.
 22. A burner according to claim 16, wherein saidblade shaped protrusions has a surface curved in a axial direction. 23.A burner according to claim 16, wherein said blade shaped protrusionshas a surface curved in an radial direction.
 24. A burner according toclaim 23, wherein said blade shaped protrusions has a surface curved inan axial direction.
 25. A burner according to claim 24, wherein theradius of curvature of said surface is the same for each of said bladeshaped protrusions.
 26. A burner according to claim 24, wherein theradius of curvature of said surface is not the same for each of saidblade shaped protrusion.